This invention relates to a carriage mechanism for a magnetic disc apparatus and, more particularly, to a carriage mechanism incorporating a rotary type actuator.
Hard disc apparatuses normally use a carriage mechanism having a rotary type actuator. This type of carriage mechanism comprises an arm, the central part of which is rotatably supported, a suspension fixed to one end of the arm and holding a magnetic head, and a voice coil motor mounted on the other end of the arm, for rotating the arm. The magnetic head has a slider which moves above a disc (a magnetic recording medium) and is provided with a read/write gap. When the arm of the carriage mechanism is rotated, the slider moves, in a floating manner, over the surface of the rotating disc to a desired track, and is positioned thereabove.
In recent years, there has been growing demand for hard disc apparatuses of increased access speed, as well as for reduction of the size and weight of the main components making up these apparatuses. With the aim of meeting these requirements, a rotary carriage mechanism of a straight type has been developed in which the slider, the suspension, and the arm are coupled to one another so that their principal axes are in alignment with one another and pass through the rotational center of the arm. By virtue of this configuration, the distance from the rotational center of the arm to the magnetic head can be reduced, thus decreasing the moment of inertia of the section which extends from the rotating center to the magnetic head. As a result, access time can be reduced, as can the size and weight of the apparatus. However, when this type of carriage mechanism uses either a composite type or a thin-film type magnetic head, the following problems arise:
The read/write gap of the above-mentioned types of magnetic head is situated in an offset position, with the center of the gap being shifted a specified amount with respect to the principal axis of the slider. Thus, the principal axis of the gap (a line which passes through the center of, and extends in the lengthwise direction of the gap) does not pass through the rotational center of the arm. Consequently, when a carriage mechanism constructed thus is employed in a disc apparatus using the servo surface servo method, the timing of readout of servo data by the servo head will differ from track to track. Thus, the positioning accuracy of the magnetic head is reduced.
Compared with a monolithic magnetic head, in which the principal axis of the slider is aligned with the axis of the gap, the composite type and the thin film type magnetic heads are superior in such characteristics as crosstalk and sound-to-noise ratio and, as a result, their use has been growing in recent years. This being so, a carriage mechanism is then called for which is compatible with a composite type or a thin film type magnetic head and is capable of positioning such a head with high accuracy.
The smaller the size of a rotary type carriage mechanism, the larger the yaw angle of the magnetic head becomes. Any increase in the yaw angle of the magnetic head results in it having reduced floating stability during operation. Consequently, if a carriage mechanism such as is disclosed in, for example, Japanese Patent Publication No. 86-51678, is employed, without modification, in a compact hard disc apparatus using 3.5-inch discs, its magnetic head will have reduced floating stability, greatly increasing the possibility of the magnetic head or disc being damaged during operation.